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instcombine: alloca: Limit array size type promotion

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Move type promotion of the size of the array allocation to the end of
`simplifyAllocaArraySize()`.  This avoids promoting the type of the
array size if it's a `ConstantInt`, since the next -instcombine
iteration will drop it to a scalar allocation anyway.  Similarly, this
avoids promoting the type if it's an `UndefValue`, in which case the
alloca gets RAUW'ed.

This is NFC when considered over the lifetime of -instcombine, since
it's just reducing the number of iterations needed to reach fixed point.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@232201 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Duncan P. N. Exon Smith 2015-03-13 19:34:55 +00:00
parent 95ff656ae0
commit 5c71858076
1 changed files with 9 additions and 9 deletions
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18
lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
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@ -169,15 +169,6 @@ static Instruction *simplifyAllocaArraySize(InstCombiner &IC, AllocaInst &AI) {
if (!AI.isArrayAllocation())
return nullptr;
// Ensure that the alloca array size argument has type intptr_t, so that
// any casting is exposed early.
Type *IntPtrTy = IC.getDataLayout().getIntPtrType(AI.getType());
if (AI.getArraySize()->getType() != IntPtrTy) {
Value *V = IC.Builder->CreateIntCast(AI.getArraySize(), IntPtrTy, false);
AI.setOperand(0, V);
return &AI;
}
// Convert: alloca Ty, C - where C is a constant != 1 into: alloca [C x Ty], 1
if (const ConstantInt *C = dyn_cast<ConstantInt>(AI.getArraySize())) {
Type *NewTy = ArrayType::get(AI.getAllocatedType(), C->getZExtValue());
@ -209,6 +200,15 @@ static Instruction *simplifyAllocaArraySize(InstCombiner &IC, AllocaInst &AI) {
if (isa<UndefValue>(AI.getArraySize()))
return IC.ReplaceInstUsesWith(AI, Constant::getNullValue(AI.getType()));
// Ensure that the alloca array size argument has type intptr_t, so that
// any casting is exposed early.
Type *IntPtrTy = IC.getDataLayout().getIntPtrType(AI.getType());
if (AI.getArraySize()->getType() != IntPtrTy) {
Value *V = IC.Builder->CreateIntCast(AI.getArraySize(), IntPtrTy, false);
AI.setOperand(0, V);
return &AI;
}
return nullptr;
}